We propose to isolate new growth factor or growth factor receptor genes, based upon their linkage to a cluster of such genes on human chromosome 5. A long range comparative physical map of the known genes within this region will be compiled, and large DNA fragments on which two or more of these genes reside, will be identified. Probes specific to these fragments will be isolated using a combination of size selection and innovative cloning technologies. This mixture of probes will then be used to screen cDNA libraries from appropriate tissues in order to identify candidate genes. If new growth factor or growth factor receptor genes could be isolated in this manner, these could be of considerable importance in the treatment of a number of hematopoietic disorders and various forms of neoplasia.